Use appropriate macosx_version_minimum value while compiling metal shaders

If OpenJDK is built on BigSur with Xcode12.5 then a lot of AWT & Swing tests failed with the following message on machines (e.g. macOS10.15) with Xcode <=12.4 or without Xcode:

#section:main
----------messages:(5/257)----------
command: main -Dsun.java2d.uiScale=1 bug6796710
reason: User specified action: run main/othervm -Dsun.java2d.uiScale=1 bug6796710
Mode: othervm [/othervm specified]
Additional options from @modules: --add-modules java.desktop
elapsed time (seconds): 0.592
----------configuration:(3/40)----------
Boot Layer
  add modules: java.desktop

----------System.out:(0/0)----------
----------System.err:(1/307)----------
2021-10-25 05:36:42.170 java[6916:107817] Failed to create pipeline state, error Error Domain=CompilerError Code=1 "Function frag_col has a deployment target which is incompatible with this OS." UserInfo={NSLocalizedDescription=Function frag_col has a deployment target which is incompatible with this OS.}

The issue was observed in Metal configurations, the tests passed well in OGL configurations

Steps to reproduce
$ jtreg -testjdk:$JDK_HOME -javaoptions:'-Dsun.java2d.metal=true' test/jdk:jdk_awt test/jdk:jdk_swing

The tests pass successfully in case -Dsun.java2d.metal=false

Note: adding --with-macosx-version-max=10.12.00 to configure does not resolve the issue.